Puzzling Adventures Warm-Up Solution - September 2008

The 24-km portion would take 3 hours (24 km at a land speed of 15 - 7 = 8 kmh) and would cost 15 kWh (5kW * 3 hours).
The 18-km portion would take 1.38 hours (18 km at a land speed of 15 - 2 = 13 km/hr) and would cost 6.92 kWh.
The 30-km lake would take 2 hours and cost 10 kWh.
So the total time is: 3 + 1.38 + 2 = 6.38 hours.
The total energy is: 15 + 6.92 + 10 = 31.92 kWh.

ABOUT THE AUTHOR(S)

Dennis Shasha is at the Courant Institute of Mathematical Sciences, New York University. His most recent puzzle book, Puzzles for Programmers and Pros, was published in 2007 by John Wiley and Sons/Wrox.

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